Method and apparatus for regulating the speed of a tape

ABSTRACT

In an operational mode in which the tape should come to a stop at predetermined positions, a braking process, which causes the stopping of a tape at an exact predetermined place, is provided. At the beginning of the braking process, a target waveform is determined in dependence on the tape speed, and the values of the speed are controlled or regulated in accordance with the waveform. Control of a slow motion mode of a video tape can also be provided.

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus forregulating the speed of a tape for the recording and/or reproduction ofitems of information, such as a video tape for example, in anoperational mode in which the tape is intended to come to a stop atpredetermined positions.

BACKGROUND OF THE INVENTION

Known operational modes in which a tape for the recording and/orreproduction of items of information should come to a stop atpredetermined positions are, for example, the so-called slow motion modeand the freeze frame mode of a video apparatus. Thereby, a video tape isscanned by a video head in such a way that individual items of pictureand/or sound information recorded on this video tape are read out oneach occasion for a defined time t. For this, the tape is wound so farthat the items of information for a first picture come into the spatialregion of the video head. After the time t, the tape is wound on in sucha way that items of information for a next picture are located in theregion of the video head. Later on, the reproduction of a furtherpicture can occur, and so on.

Thereby, it is important that the tape be brought to a standstill asaccurately as possible in such a way that the beginning of the currentitems of picture information always coincide exactly with the region ofthe video head. This means, in particular, that an exactly executeddelaying or braking process has to be instituted at the end of eachwinding on sequence so that a precise stopping of the tape is ensured.

Known apparatus, such as video apparatus for example, institute abraking process after a defined winding on time, during which, brakingmeans such as a motor, a mechanical brake or the like, are controlled byfixed, defined control signals. This means that tolerances, which areoccasioned, for example, by manufacturing tolerances of the apparatus,by different video tapes, by temperature effects and the like, are nottaken into account.

The object of the present invention is to further develop the course ofa braking process of the said kind in such a way that a tape for therecording and/or reproduction of items of information is brought to ahalt, as exactly as possible, at predetermined positions.

This object is achieved by a method in accordance with claim 1 and by anapparatus in accordance with the first apparatus claim.

SUMMARY OF THE INVENTION

Advantageous developments of the invention are specified in theappendant claims.

In accordance with the invention, a braking process which effects anexact stoppage of a tape for recording and/or reproduction, such as avideo tape for example, is realised in that, at the beginning of thebraking process, a target waveform is determined to which the actualvalues of the speed are controlled or regulated. These target values, orelse, their time-related waveform, may be determined for example on thebasis of the tape speed and/or position at the beginning of the brakingprocess.

Further features, advantages and details of the invention are explainedin the following embodiments with the help of the drawing. Therein

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block circuit diagram of a preferred embodiment;

FIG. 2 provides a symbolic illustration of a video tape;

FIGS. 3, 4, 6 illustrate waveforms of the speed values of a video tapefor the embodiment of FIG. 1;

FIGS. 5, 7 illustrate waveforms of the motor control voltages during abraking process.

DETAILED DESCRIPTION OF THE INVENTION

Before going into the detailed description of the embodiments, it ispointed out that the blocks individually illustrated in the Figuresmerely serve for a better understanding of the invention. Usually,individual ones or several of these blocks are combined into units.These may be realised in integrated or hybrid technology or as aprogramme controlled micro-processor or as part of a programme that issuitable for its programming.

The elements contained in the individual stages may also, however, beimplemented separately.

FIG. 1 shows the block circuit diagram of a first embodiment in which avideo recorder is symbolically indicated by 10. The latter contains afirst spool 11 from which a video tape 12 is wound onto a second spool15 over deflecting rollers 13, 14. The video tape 12 is led past a videohead 16 and a reading head 17. The speed of the tape 12 is controlled bya driving motor 18, also known as a capstan motor, which receivescorresponding control signals Sm from an electronic control device 19.The motor 18 is mechanically coupled, for example via drive belts or thelike, to a drive wheel 20 which, with a complementary roller 21, effectsthe transport of the tape 12 at a defined speed. The latter can bemeasured by means of a tachometer wheel 22 upon which there areintroduced equally spaced markings 23. The latter may be optical ormagnetic for example, and are detected by a sensor 24 which is formed asan optical sensor, Hall sensor or the like and sends its output signalFG to the control device 19.

As illustrated symbolically in FIG. 2, apart from the items of videoinformation 12a, control pulses 12b are also stored on the video tape 12at a predetermined position with reference to the items of videoinformation 12a. Whilst the video head 16 is reading out the videosignals 12a and passing them on via appropriate processing stages 24 toa display device 25, such as a television set for example, the readinghead 17 receives the control signals 12b. In addition, it may beconstructed in such a way that it receives audio signals from the tape12. The signals from the reading head 17 are led to the electroniccontrol device 19 and to the processing stages 24.

The uppermost curve of FIG. 3 shows the waveform of the reference speedVs of the tape 12 during a slow motion mode. After a video picture hasbeen read out for a given period of time, the motor 18 is controlled bythe control device 19 at a time point to in such a way that the tape 12accelerates from v0 =0 up to v1 in a time interval t0-t1 and thereafter,it is then transported further at this speed. At a time point t2, thereading head 17 detects the control signal 12b and the motor is brakedby the control device 19 at a time point t3. The reference waveform ofthe braking is such that the tape 12 comes to a stop (v0) at the timepoint t4. Thereafter, the tape 12 remains still for a given time periodt4-t0.

During the whole operation, the control device 19 is receiving thesignals FG wherein the number of pulses per unit of time increases withincreasing speed v. Thereby, the number of pulses appearing is a measurefor the actual number of revolutions of the drive roller 20 and thus, inessence, also for the actual length of the transported tape 12. Theseparation in time between two pulses is a measure for the actual speedof the drive roller 20 and thus, in essence, also for the tape 12.

In order to regulate the actual values i.e. a real progression, of thespooled-on length of the tape and of the speed Vi as exactly as possibleto the reference values, the embodiment functions in accordance with themethod described more fully below.

What is essential for the slow motion mode, for a freeze frame mode andthe like, is that the tape 12 always comes to a stop at a predeterminedposition at the time t4. In order to compensate errors in the startingphase (t0-t3), a counter is started upon the appearance of the pulse 12bat the time point t2. The counter is contained in the control device 19and counts back by one unit starting from a number q with each new pulseof FG. That is to say, with the appearance of the pulse 12b, the controldevice 19 has a value available which is a measure for the remaininglength of tape up to the stopping of the tape 12. When the backwardlycounting counter has reached a value p, the control device 19 theninstitutes the braking process. The following description of the methodof operation is limited, in essence, to the regulation of the tape speedduring the braking process in the time period t3-t4.

It is to be assumed that at the time point t3, the actual speed V1i doesnot coincide exactly with the reference value V1s. The actual value V1iof the speed may lie above V1s for example, as is illustrated in FIG. 4.In order that the tape 12 is braked at the latest at the time point t4in such a way that it comes to a stop with the remaining length of tapep, the waveform of target speeds Vz(t), to which the real actual valuesVi(t) of the speed are regulated, is determined by the control device19. It is assumed in FIG. 4 that the waveform of the target speeds Vz(t)corresponds exactly to the waveform of the actual speeds Vi(t).

As already mentioned, it is essential that the tape 12 comes to a stopat a predetermined position. In principle, the speed waveform therebyonly plays a secondary role. However, since

vi(t)=dLi/dt

where: Vi(t)=the actual speed of the tape and

dLi/dt=the wound on length of the tape per unit of time,

the length Li of the wound on tape can also be determined through theregulation of the speed Vi(t). The desired regulation of the length Liis achieved in that a regulation with respect to the integral betweenthe curve Vi and the curve Vs is realised. That is to say, the area Aillustrated in FIG. 4 has to be equal to the area B.

Expressed mathematically, this may be achieved through the followingconsiderations. The reference speed Vs(t) in the time interval t3-t4 isdetermined by the following equation:

    Vs(t)=V1s-k*t; k: slope.                                   (1)

The slope k may be the same or different for different modes ofoperation such as for example, normal slow motion, slow motion of longplay recordings, play back after a pause, automatic search or the like.If k is the same, then one needs less storage and the method stepsdescribed more fully hereinafter are similar for the said modes ofoperation.

The waveform of the target values Vz(t) is given by

    Vz(t)=V1s+DV-(k+DK)*t                                      (2)

where

V1+DV=V1i and

k+DK: slope of Vz(t)

The control device 19, in which the waveform of Vs(t) is stored,determines, by means of an elementary mathematical calculation

    Dk=DV/V1s*(2+DV/V1s)*k.                                    (3)

A corresponding regulation of the actual values Vi(t) to the waveform ofthe target values Vz(t) is effected by the control device 19 throughevaluation of the pulses FG and by control of the motor 18. However, itis also possible to only control the motor 18 instead of regulating it.

If one assumes a voltage control for the control of the motor 18, thenthe value progression of the corresponding control voltage U(t) can bedetermined on the basis of the following considerations.

One starts from the generally known equation

    U=R*I+E+L*dI/dt                                            (4a)

where

R: internal resistance

I: the current flowing through the motor windings

E: mutual induction voltage,

L: the inductance of the motor wherein

E=a*v

a: motor constant,

v: rotational speed of the motor.

Since one can usually assume that L/R is substantially smaller than themechanical time constant of the motor, the equation (1a) simplifies to

    U=R*I+E                                                    (4)

The current I is proportional to the torque D, i.e.

    I=c*D(c=constant),                                         (6)

and the torque D is

    D=r+J*dv/dc                                                (7)

where

r: measure for the frictional loss

J: torque mass

v: rotational speed of the motor.

There thus results

    U-r=a*v+b*dv/dt                                            (8)

    where b=c*J*R=constant.                                    (8a)

If a speed Vs(t)=V1s-k*t (see equation (1)) is to be realised, then thecontrol signal U(t) has to have the form

    U(t)=f*t+g                                                 (9)

(see also equation (8)). Conversely, there results from a control of theform

    U(t)=f*t+g                                                 (9)

by solving the equation (8) for Vs(t)

    Vs(t)X+Y*t*C*exp(-t*a/b).                                  (10)

where

X=a+f

Y=(g*a-f*b)/a²

C: constant, which is determined by the starting conditions.

At the time t=0, there results

    V=Y+C=V1s+DV.                                              (11)

In order to attain C=0, one has to have

Y=V1s+DV.

Consequently, for the realisation of the waveform Vs(t) as isillustrated in FIG. 4, there results the following waveform Us(t) forthe control voltage of the motor 18, as is illustrated in FIG. 5:

for the initiation of the braking process at the time point t3, Us jumpsfrom a starting value U1s, which is required for the realisation of thetape speed V1s, up to a value

U2s=U1s-b*k; (b constant, see above)

thereafter, U is regulated down with the slope

-a*k

wherein

a, b are the already mentioned motor constants and

k is that particular value with which the reference speed Vs(t) is alsobrought down in the time interval t3-t4 (see equation (1)).

There thus arises for the waveform of U(t) in the time interval t3-t4:

    U(t)=U1s-b*k-a*k*t.                                        (12)

The motor constants a and b are given magnitudes and can be easilydetermined. Therewith, the jump and the ensuing waveform can also beeasily determined. If it arises, as already explained with the help ofFIG. 4, that the tape 12 does not have the speed V1s at the time pointt3 but rather a speed V1i deviating therefrom, then the value k+DK is tobe used in the above equation instead of k.

As a rider, it should be mentioned that the transmission path betweenthe motor 18 and the tape 12 must also be taken into account in theseconstants.

Moreover however, tolerances for the two constants a, b are also to betaken into account. These depend on the video apparatus, the videocassette being used, the temperature and the like. The values which arerelevant at any one time can be newly determined by adaptive processes.One example of such a process is described below.

The waveform U(t) in FIG. 5 can be realised either by a pure control orby a combination of control and regulation. Preferably to this end, thejump and/or the ensuing waveform or a part thereof, can be controlled tobegin with. That is to say, corresponding step functions may be used.The further waveform can be optimised by a regulation through which aregulated jump Sp and a regulated waveform Sl is determined. From thethereby resulting total waveform Sp+Sl in the interval t3-t4, theconstants a and/or b can be determined more accurately. Thecorresponding values of these constants may be stored for furthercontrol processes. Thereby, a dependence of these values on the videotape being used, on its position, on the temperature, on the videoapparatus and/or on various parameters can be taken into account.Corresponding starting values may already be stored, from the beginning,in the factory.

The values of a and b may also serve for the purpose of setting otheroperating quantities. Such an operating quantity is for example, thelimiting of the current for the control of the motor 18. Thisconsideration arises by reason of the equations (4) and (5).

The following processes for the correction of a and b are mentioned inparticular:

1. The value determined by regulation

Sl=dU/dt

is regulated such that

dv/dt=-(k+DK)

If the actual value is called

dv/dt=k_(is)

and the actual value

a=a_(ref),

then at any one time

Sl=a_(ref) *k_(is),

wherein k_(is) and Sl are known. Thereupon

Sl/k_(is) is formed. If

Sl/k_(is) is greater than a, then a is increased; in case

Sl/k_(is) is smaller than a, then a is reduced

Preferably, a is refined step by step and not calculated in accordancewith the relationship a=Sl/k_(is).

If b is not determined correctly, then there results an exponentialremainder and the following applies

Sl approximates to a_(ref) *k_(is).

For this reason, relative steps of a i.e. da/a, should be smaller thanrelative steps of b as explained in the process described under 2 below.

2. In case the waveform of the regulated control voltage U(t) at thebeginning of the interval t3-t4 is greater than at the end of thisinterval and in case the actual speeds Vi correspond to the targetspeeds Vz at the beginning and at the end, then a value b1 is replacedby a value b2 which is larger than b1: and vice versa. (This resultsfrom the necessary correction of the exponential terms).

As a rider, it should be mentioned that in the description of the methodup to now, a rigid coupling of the tape 12 to the motor 18 was assumed.In practice however, there will be divergences from this which may becaused for example, by a slippage, by elasticity of a drive belt and/orof the video tape 12 and the like. These divergences may be recognised,for example, on the basis of pulses of the signal FG registered at agiven time point and they may be balanced out for example, by acorrection of the time point t3 and/or by an alteration of the referenceslope k.

The description of the method up to here, which may be realised by theembodiment of FIG. 1, can then be utilised in particular when a verysmall resolution due to the pulses of the signal FG is present and/orwhen a coarse time resolution is available. If better conditions exist,then the method described below, which can likewise be realised by theembodiment of FIG. 1 with an appropriate arrangement of the controldevice 19, is utilised in preference.

As is apparent from FIG. 6, in the method now being described, acomplete balancing out of the effect of the different speeds V1s, V1ioccurs not at the very end of the braking process but rather, earlier,at a time point t5 which may lie anywhere in the time interval t3-t4.

This has the advantage that possible divergences for the already unwoundlength of tape can still be compensated by a regulation process in thetime interval t5-t4. Moreover, at the time point t4, a transition intothe state of rest always takes place with substantially the same speedwaveform independently of the speed V1i. Thereby, possible fluctuationsin the regulation are disregarded. By so doing, the differences due toerrors caused by slippage and elasticity are similar. For one type ofapparatus, these can be partly determined in advance in dependence onthe temperature, the tape length, the position of the tape and/or thelike and they can be partly compensated by simple measures. Since theactual braking time corresponds to the braking time given by thewaveform of Vs(t), the synchronisation with the video head 16 isimproved.

In a preferred embodiment, t5 is selected in such a way that it lies twothirds within the time period t3-t4. Initially, the determination of thewaveform of Vz(t) in the interval t3-t6 occurs in accordance with (seeFIG. 6)

Vz(t)=V1s+DV-(k+d'k)*t.

This means that d'k has to be determined. A minimum value for d'k, whichis used in case t5 should be identical with t4, is

d'k_(min) =(1+2⁰.5)*k*Dv/V1s.

However, in the event that the length of the phase t5-t4 should amountto one third of the total braking time t3-t4, as in the preferredembodiment, then

d'k=1.5*(1+2⁰.5)*k*DV/V1s.

The error in the unwound length of tape is at its greatest when thecurve Vz(t) cuts the curve Vs(t) i.e. when

V1s-k*t=V1s+DV-(k+d'k)*t.

The corresponding time point t7 thus occurs at

t7=t3+DV/d'k.

The time point t6, at which the maxi error is half compensated, isarrived at from

t6=t3+t7*(1+1/2⁰.5).

However, the time point t6 may also be determined by a regulatingprocess in such a way that the maximum error is half compensated at thistime point. The correction of the residual error in the range t6-t5 isachieved by a waveform of the curve Vz(t)

Vz(t)-M-(k-d'k)*t

where M=V1s-Dv*(1+2⁰.5).

Thereby, t5 is given by

t5=t3+t7*(1+2⁰.5).

From the time point t5, at which the error in the advanced tape lengthis theoretically zero, the curve Vz(t) proceeds in the same way as thecurve Vs(t). The real actual speed values Vi(t) are regulated on thecurve Vz(t). For this, generally known regulating processes may be usedwhich provide for a proportional, integral and/or differentialregulation. In this embodiment, possible regulation divergencies are sotiny that they are not illustrated in FIG. 6.

FIG. 7 shows the waveform of the control voltage of the motor 18 for themethod illustrated in FIG. 6.

A voltage jump is provided for each alteration of the slope of Vz(t) forthe compensation of the already mentioned exponential terms. At the timepoint t3, there follows a first jump Sp1 with

Sp1=-b*(k+d'k)

and thereafter a waveform Sl1 with

Sl1=-a*(k+d'k).

At the time point t6, a second jump Sp2 is provided with

Sp2=+b*2*d'k

and a second waveform Sl2

Sl2=-a*(k-d'k).

After the third jump Sp3 at the time point t5

Sp3-b*d'k

there follows the waveform Sl3

Sl3=-a*k.

In the second embodiment too, the waveform U(t) can be realised eitherby a pure control or by a combination of control and regulation.

In a further version of this embodiment, the time point t6 may bedisplaced for later braking phases to the time point t5 in dependence onthe actually remaining residual tape length L(t5) or in dependence uponthe difference

DL(t6)=L(t5)-L_(ref) (t5)

in accordance with the following conditions:

a) if DL(t5)*d'k is less than zero, t6 is brought forward,

b) if DL(t5)*d'k is greater than zero, t6 occurs later.

A truncation criterion for t6-t5 can be, if V(t)=Vz(t) or L(t)=Lz(t).

Alternatively to the correction of t6, the following procedure may becarried out in the interval T6-t5. The actual position Li and the actualspeed Vi are measured at a time t' which lies anywhere within theinterval t6-t7. A new value k' is determined for this time t' which isused instead of the previous value k-Dk. If the curve v for dV/dt=-k'meets the reference speed Vs=V1s-k*t at t5, then so too should thepositions L(t) and L_(ref) (t). The determination of the appropriatevalue k' arises from the following calculation ##EQU1##

An offset can be added to this k' which serves the purpose of balancingout the error in the position following the overshoot after t5. Thisoffset can be corrected from one step (t0-t4) to the other.

In the last phase (t5-t4) of the braking process, there may be provideda regulation by reason of the speed waveform or, in addition, a furtherregulation with respect to the residual tape length may also beeffected.

Versions of the said embodiments may have at least one of the followingvariations:

the exact braking of the video tape 12 may also serve for the recordingof items of information. These may be first time recordings or otherthings such as for example, the dubbing of or fading-in to previouslyrecorded pictures;

instead of bringing the video tape 12 to a halt, other tapes may also bestopped at predetermined positions. These tapes may be suitable for therecording and/or reproduction of items of information such as data,pictures and/or sound on the basis of optical, electric and/or magneticmethods;

Errors, which are caused by slippage, elasticity or the like of the tapeor by other means in the apparatus, may be balanced out by altering thebeginning of the braking phase (t4) and/or by altering the waveformVs(t) or Vz(t). Thus for example, the waveform Vs(t) may be chosen asfollows:

Vs'(t)=k/(T+t)² ; T is constant;

errors during read-out of the items of tape information may bedetermined automatically;

the waveform of Vs(t) or Vz(t) may be selected in such a way thatmathematical processes can be carried out more simply;

the braking phases may also be used for a rapid search and/or for arapid rewind in the case that the tape is to be stopped at apredetermined position;

in case the motor 18 is not controlled by a direct voltage but rather,by a pulsed voltage such as for example, by pulse width modulation(PWM), pulse length modulation (PLM), or by other control signals, thenthe conversion of the speed waveforms into the control signals is to beundertaken correspondingly;

the waveform of the control signals for the motor 18 may also be usedfor the purpose of realising a pure regulation. That is to say that ajump at t3, t5 and/or t6 is not carried out. A preferred solution ofthis idea is the following consideration. Starting from the equation

    L.sub.ref =V1s*t-(1/2)*k*t.sup.2

where: L_(ref) : reference tape length,

which results from the equation (1), the appertaining actual tapeposition L_(is) (p, p-1, . . . p-n, . . . 0) and the appertaining time(t3, . . . t4) is determined for each pulse of the signal FG. Thedifference value

DL=L_(ref) -L_(is)

serves for example, for the determination of the following regulationmagnitudes for a PID regulation:

Kp*DL+Kd*(DL/dt)+Ki*Intergral(Dl*dl)

where

Kp, Kd, Ki: regulating constants for proportional, differential orintegral regulation

Integral (..): single or double integral.

The use of the double integral has the advantage that the correspondingregulation is quicker and more accurate.

What is claimed is:
 1. A method for controlling the speed of a tape forrecording and/or reproducing items of information, wherein, from a firsttape speed and from a first time point,said tape is caused to stop at apredetermined position corresponding to a last time point, defining abraking period, said method comprising the steps of: providing areference speed waveform having reference values as a function of timeassociated with the speed of said tape between said first time point andsaid last time point corresponding to the stop position of said tape;measuring the actual speed of the tape at said first time point;determining a target waveform based on the measured value of the actualspeed, wherein said target waveform has an integral value of the areaunder said target waveform substantially corresponding to the integralvalue of the area under the reference waveform; and regulating theactual speed of said tape during the time period defined between saidfirst and last time points to correspond to said target waveform speed.2. Method according to claim 1, further comprising merging the targetwaveform into the reference waveform before the ending of the brakingperiod.
 3. Method according to claim 2, wherein the step of controllingfurther comprises generating control signals for controlling a motor fordetermining the speed of the tape before said braking period, whereinthe initiation of said braking period occurs in accordance with thetarget waveform.
 4. Method according to claim 3, wherein the step ofcontrolling further comprises adaptively altering the actual speed valuecorresponding to the curve of said target waveform by steppedadjustments to a control variable to compensate for deviations betweensaid target and reference waveforms.
 5. Method according to claim 4,further comprising the step of removing errors which are caused byelasticities or by slippage of the tape by modifying said first timepoint defining the beginning of the braking process and/or modifying thecurve of said target waveform.
 6. Apparatus for controlling the speed ofa tape for the recording and/or reproduction of items of information,wherein, from a first tape speed and from a first time point, said tapeis caused to stop at a predetermined position corresponding to a lasttime point, during a braking process defined by said first and last timepoints in accordance with a predetermined reference speed waveform, saidapparatus comprising:tachometer means for measuring the actual speed ofsaid tape at said first time point; a drive for effecting transport ofsaid tape at a defined speed; and control means for controlling saiddrive and regulating the actual speed to cause said tape to stop at saidpredetermined position, said control means responsive to said measuredtape speed for determining a target waveform of speed values in order tocontrol or regulate the actual speed values during said braking processin accordance with said target waveform, wherein said target waveform ofspeed values has an integral value of the area under said targetwaveform which substantially corresponds to the integral value of thearea under the reference speed waveform.
 7. Apparatus according to claim6, wherein the target waveform of speed values merges into saidreference waveform of speed values before the ending of the brakingprocess.
 8. Apparatus according to claim 6, wherein said drive includesa motor for driving said actual tape speed, and wherein said controlmeans provides control signals to said motor to initiate said brakingprocess, said control means operative to determine the speed of saidtape before the braking process in order to permit braking to occur inaccordance with the target waveform.
 9. Apparatus according to claim 8,wherein said control means further comprises means for adaptivelyaltering the actual speed values corresponding to the curve of saidtarget waveform by stepped adjustments to a control variable tocompensate for deviations between said target and reference waveforms.10. Apparatus according to claim 9, wherein errors which are caused byelasticities or by slippage of the tape are balanced out by modifyingthe determined first time point defining the beginning of the brakingprocess and/or by modifying the curve of the target waveform.
 11. Amethod for controlling the speed of a tape from a first speed at a firsttime to cause said tape to stop at a predetermined positioncorresponding with a second time, defining a braking period, said methodcomprising:measuring actual speed of a tape at a time before said firsttime; determining a target speed waveform for said braking period, saidtarget speed waveform representing a voltage control or time controlvariable and comprising a controlled time interval including said secondtime and during which a generally constant slope voltage is applied tosaid capstan motor; and controlling a capstan motor driving said tapefor controlling actual speed of said tape in accordance with said targetspeed waveform during said braking period.
 12. Method according to claim11, where in said target speed waveform further comprises a generallyconstant reverse voltage in combination with said slope voltage. 13.Method for controlling speed of a tape comprising:coupling a tapetransport motor to a tape for driving said tape; applying a controlsignal to said tape transport motor during a given time period; varyingsaid control signal at a substantially constant slope; and effecting asubstantially constant slope deceleration of said tape by said varyingof said control signal at said substantially constant slope during saidtime period.
 14. Method according to claim 13, wherein said controlsignal is a control voltage, said transport motor comprises a DC motor,said control voltage is jumped from a first value to a second value atthe start of said time period, said control voltage is varied inaccordance with said constant slope from said second value to a thirdvalue at an end of said time period, and said control voltage is jumpedfrom said third value to a fourth value at the end said time period. 15.Method according to claim 14, wherein said second value is greater thansaid first value, said third value is less than said second value, andsaid fourth value is less than said third value.
 16. Method according toclaim 15, wherein said time period is within the first 2/3 of a brakingperiod during which said tape is brought to a stop at a predeterminedposition after said time period.
 17. Method according to claim 16,wherein said time period is within a portion of a braking period endingwith said tape being stopped at an intended position after said timeperiod, said control signal in accordance with said substantiallyconstant slope effecting said substantially constant slope decelerationof said tape to a desired speed at the end of said time periodcoinciding with a desired slope in deceleration of said tape for theremainder of said braking period.
 18. Method according to claim 17,wherein said time period is preceded by a first deceleration of saidtape and succeeded by a second deceleration of said tape, transitionsfrom said first deceleration to said substantially constant slopedeceleration during said time period and from said substantiallyconstant slope deceleration to said second deceleration being effectedby jumps in said control signal.